Aluminum galling situation

A. Since you did not tell us what the two parts are, it is rather difficult to say anything definite. As far as lubrication, consider using a high vacuum silicon grease. It sticks to the part far better than any other lubricant that I know of. Another option is to use a dry film lube (a non graphite one). They make a spray on, that does not have to be baked for aluminum. I prefer the baked on type, at least for the initial application. This stuff is good for several take apart cycles and the non bake could be added by the customer. Of course, if this is for surgical or space application, switch to at least one different metal.

A. I would use a heli-coil in your part, it would add to the strength of the al threads, plus help your galling issue.

A. Hi, Charlie.

Someone else will have to give you a more complete, more complicated rule of thumb. The simplest way to look at it that I know of is to consider it a cold welding issue, so things tend to gall against themselves, and the list of such materials includes glass, aluminum, and most stainless steels :-)

A. To avoid the galling problem, one Al part can be coated with oxides by using electrolytic plasma process.

A. Why not hardcoat the threaded part?

A. Dear Charlie,

Anodize the smaller part, and impregnate the oxide layer in melted paraffin or oleic acid, choose the best thickness by trial and error and extending the impregnating time.

A. The parts may be conversion coated with a non-chromate based system and then e-coated with a non-galling coating (less than 1 mil).

A. Hi guys. sorry this input is rather late. I have found that Anhydrous Lanolin is very good with fine aluminium threads, and does appear to minimise galling.
As a matter of interest, it is used on rifle scopes where the tube diameter is around 1 inch (25 mm) and the thread pitch is very fine (around 0.3 mm).
The downside is that lanolin gets a bit tight at low temperatures.

I often machine components with mating threads, out of aluminium and Acetal plastic.
The acetal is an engineering plastic, quite expensive, but slides beautifully against aluminium. However, it might be a bit soft for some applications.
I use a lot of C-mount, CS-mount, and M12 board lenses for cctv components, and their fine threads run smoothly. They appear to be black anodised, but I am not 100% sure it is anodising.
Gary - New Zealand.

A. The problem with anodizing is it's very thin, and can wear off quickly. This same problem exists with semi auto .22 pistols, that have both an Aluminum slide wearing against an aluminum frame. Without proper and correct lubrication they can gall and seize up, disabling the pistol.

The solution is using the correct lubricant / anti seize to prevent these 2 soft, similar metals from galling. This product was designed for that purpose: zinc anti-seize compound [on eBay or Amazon].

A. You could try hard coat anodizing which is harder and thicker than ordinary sulfuric acid anodizing.

A. The cheapest, and arguably the most effective solution would be to wax the parts. The commercial formulations are often called "bonded solid film lubricants."

A. You might be better off with different coatings on opposing surfaces.

Anodize against electroless nickel. Uncoated/EN or anodize.

And, as Tom suggested, a bit of lubricant may be a help.